This invention pertains generally to solid state amplifiers and in particular to amplifiers of such type which use high power IMPATT diodes and which are adapted to broadband operation.
Solid state amplifiers using devices such as IMPATT diodes with inherently high reliability, low cost, small size, light weight and low voltage requirements are now being considered for use in many radar and navigation systems. However, the low power capability of known types of IMPATT diodes (or other similar devices) in the microwave portion of the radio frequency spectrum has, heretofore, limited the application of the solid state amplifier with a single IMPATT diode to low power applications. When the particular application requires a power level higher than is possible with a single IMPATT diode, it is sometimes feasible to combine the power outputs of several IMPATT diodes to attain the requisite power level. For example, a number of IMPATT diodes may be coupled to a resonant cavity in any one of many known ways so that the outputs of such diodes are added together in phase. Unfortunately, however, the operating bandwidth of any such arrangement is determined by the bandwidth of the resonant cavity; as a result, then, if an operating bandwidth of more than a few percent of the operating frequency is required, no combining arrangement using a resonant cavity is feasible.
Other known types of power combiners include the so-called series constrained binary combiner and the N-way Wilkinson combiner, which is described in an article entitled "An N-Way Hybrid Power Divider" by E. J. Wilkinson, IRE Transactions on Microwave Theory and Techniques, January, 1960. However, any known series constrained binary combiner is large, is power limited, and is subject to relatively large insertion losses, while the Wilkinson combiner requires relatively large power dissipating isolation resistors (which are difficult to implement) to operate properly at a high power level.
Still another known type power combiner is the so-called radial line power combiner wherein there is a low loss and a high degree of symmetry. However, to be of any practical value, such a power combiner must be provided with mode suppression and isolation means. Thus, one known form of radial line power combiner (described in an article appearing on page 9 of the October 1977 issue of "MICROWAVES") employs isolation resistors between adjacent arms of the combiner. As mentioned hereinabove, such resistors tend to limit the performance of a combiner used in a high power application.
In another known radial line combiner a mode suppression arrangement is provided at each radial feed. Unfortunately, however, any known mode suppression arrangement is lossy and is subject to the shortcoming that the individual IMPATT diodes may lock together rather than to the input signal intended to be amplified.